1. Field of the Invention
This invention is directed to polymer devolatilization and recovery and, in certain aspects, to production of a polymer product with a residuals level of less than one thousand parts per million(ppm), the polymer product being produced from an initial polymer solution having a residuals level of up to fifty percent by weight, based on polymer weight. One particular method according to this invention is directed to the devolatilization of ethylene propylene diene monomer terpolymer (EPDM).
2. Description of Related Art
The prior art discloses a wide variety of polymer devolatilization and recovery systems and methods. Certain prior art methods have one or more disadvantages: a multi-stage process including a finishing step; required stripping of contaminants, residual solvent, and monomers; use of an immiscible fluid mixed with a flowing polymer to maintain heat transfer coefficient, increase diffusion driving force, or lower partial pressure; entrainment of polymer in overhead venting systems, known as "snowing", and polymer product flowing into venting systems, known as "vent flooding"; production of polymer product with inconsistent properties, such as a varying viscosity, or production of degraded product polymer or gels; and additional process unit operations to remove immiscible liquid or gas.
There has long been a need for an efficient, effective, single stage method for devolatilizing viscous polymers. There has long been a need for such a method which is relatively less expensive than existing methods and requires reduced capital outlay compared to existing methods. There has long been a need for such a method which produces a quality product with consistent properties without unacceptable viscosity variance, and without product degradation. There has long been a need for such a method which does not require additional stripping, an additional finishing step, or use of an immiscible fluid to maintain heat transfer. There has long been a need for such a method in which snowing and vent flooding are significantly reduced and thereby improving product quality.